Graphene's unique electronic and optical properties have made it an attractive material for developing ultrafast short-wave infrared (SWIR) photodetectors. However, the performance of graphene SWIR photodetectors has been limited by the low optical absorption of graphene as well as the ultrashort lifetime of photoinduced carriers. Here, we present two mechanisms to overcome these two shortages and demonstrate a graphene-based SWIR photodetector with high responsivity and fast photoresponse. In particular, a vertical built-in field is employed in the graphene channel for trapping the photoinduced electrons and leaving holes in graphene, which results in prolonged photoinduced carrier lifetime. On the other hand, plasmonic effects were employed to realize photon trapping and enhance the light absorption of graphene. Thanks to the above two mechanisms, the responsivity of this proposed SWIR photodetector is up to a record of 83 A/W at a wavelength of 1.55 μm with a fast rising time of less than 600 ns. This device design concept addresses key challenges for high-performance graphene SWIR photodetectors and is promising for the development of mid/far-infrared optoelectronic applications.

COMMUNICATIONIn this paper, we present a highly broadband (from visible to infrared) photodetector based on chemical vapor deposition (CVD) graphene-silicon heterostructure, together to be operated in photoconductor mode. This device shows very high responsivity (>10 4 A W −1 ) at wavelength of 632 nm, where light absorption relies on silicon. More importantly, even in the infrared region (1550 nm), where light absorption only depends on the graphene, the responsivity of our detector can be as high as 0.23 A W −1 , which is much higher those by pure monolayer graphene-based devices without optically assisted structure in this spectral region. [ 13,15,24 ] The signifi cant response is mainly due to the fact that the built-in fi eld in heterostructure can effectively prolong the ultrashort lifetime of photon-induced carriers. Besides, we also fi nd three dynamic processes in the transient response: photo-induced carriers sweeping into graphene by the built-in fi eld, electrons in the depletion region diffusion back to graphene, and photo-induced carriers in the bulk silicon diffusion to graphene. Due to the fi rst mechanism, the response time of our detector is less than 3 µs, which has not been reported among graphene photoconductor/ phototransistors. [ 1 ] The structure of graphene-silicon heterostructural photodetector is schematically shown in Figure 1 a. The start wafer we employed is a lightly doped p-type silicon wafer (>100 Ω). A thin layer of SiO 2 is grown on silicon and patterned a window on top. Then, the CVD graphene (the Raman spectra is shown in Figure S1, Supporting Information) is transferred, and both electrodes are deposited on graphene. The SiO 2 layer can avoid the overlap between the electrode and silicon. A Schottky junction is thus formed at the interface between graphene and silicon. The Fermi level differences are measured by Kelvin probe force microscopy (KPFM) in the dark. As shown in Figure 1 b, the surface potential differences (approximately similar to the work function misalignment for clean samples) between graphene and silicon, and between graphene and gold are about 0.08 and 0.16 eV, respectively. Under ambient conditions, the work function of gold is around 4.8 to 4.9 eV. [ 25,26 ] By taking the intrinsic work function of graphene (≈4.56 eV) [30][31][32] into consideration, an energy band diagram is depicted in Figure 1 c. The Fermi energy of graphene should be around 0.16 to 0.26 eV. A built-in fi eld forms at the surface, which directs from silicon to graphene. The graphene not only functions as the charge transport channel, but also works as the light absorber for the light with photon energy lower than the Fermi energy.In the visible light experiment, the photodetector is characterized by the laser at wavelength of 625 nm. Optical attenuators are introduced to change the input power. DOI: 10.1002/adom.201500127Graphene is thought to be an ideal material for novel photodetectors due to its unique properties. [1][2][3] For example, its zero bandgap affords the benefi t of ultr...

We demonstrated strong optical absorption in a graphene integrated silicon slot waveguide. Due to the increase in light intensity and decrease of optical mode confinement in the silicon slot, the graphene experienced an increased interaction to the in-plane light. A waveguide absorption of 0.935 dB μm(-1) was measured at 1.55 μm wavelengths. Based on the graphene-on-silicon slot waveguide, a compact and high-responsivity photodetector was demonstrated. Benefited from the lack of efficient electron cooling in the suspended graphene and the intensity enhancement effect in the nano slot, a maximum responsivity of 0.273 A W(-1) was achieved in the telecommunication band.

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Waveguide photodetectors integrated with graphene have demonstrated potential for ultrafast response and broadband operation. Here, we demonstrate high-performance chemical vapor deposited graphene-on-silicon nitride waveguide photodetectors by enhancing the absorption of light propagating in the transverse-magnetic mode through a metal-graphene junction. A doubling in responsivity is experimentally observed. In our zero-biased metal-graphene junction, a 15  mA W intrinsic responsivity and a 30 GHz bandwidth are achieved at ∼1550  nm. The results are comparable to those obtained from the best pristine graphene-based photodetectors. Our work enables new architectures for high-performance optoelectronic devices based on the graphene-on-silicon nitride platform.